1. Technical Field
The present invention relates to a technique for detecting contact.
2. Related Art
Display devices having a function of detecting the contact between an object, such as a finger or a pen, and a screen have been known. For example, JP-A-2007-47851, JP-A-2006-40289, and JP-A-2006-189868 disclose a first technique that detects a variation in the capacitance of a capacitive element including two electrodes opposite to each other and an electro-optical material, such as liquid crystal, interposed between the two electrodes to detect the contact between an object and a screen. In addition, for example, JP-A-2005-72126, JP-A-2004-119494, and JP-A-2008-27292 disclose a second technique that detects a variation in the amount of light incident on an optical sensor to detect the contact between an object and a screen.
In the first technique, capacitance detecting units each including the capacitive element including two electrodes opposite to each other and an electro-optical material interposed between the two electrodes are provided in a display device. One of the electrodes is provided on a surface of a first substrate facing a second substrate, and the other electrode is provided on a surface of the second substrate facing the first substrate. In this structure, it is considered that a plurality of capacitance detecting units are provided in the display device in order to detect a contact position between the object and the display device. When the object contacts the display device, the substrate is curved, and a gap between the electrodes varies. The capacitance detecting unit disposed closest to the contact point detects a variation in capacitance corresponding to the variation in the gap between the electrodes and detects the contact of the object. However, the curving of the substrate causes other capacitance detecting units to detect the contact of the object. As a result, an excessively large area is likely to be specified as the contact position between the object and the display device. That is, it is difficult to accurately detect the contact position of the object.
In the second technique, the optical sensor is provided in the display device. In this structure, for example, when an object, such as a finger, with a shadow approaches the screen, the amount of light incident on the optical sensor is changed by the shaded area even though the object does not contact the screen. As a result, it may be determined that the object contacts the screen, which is a detection error. Therefore, it is difficult to accurately determine whether the object contacts or approaches the screen. That is, there is a concern that the contact position of the object will be erroneously specified.